Re: [PATCH] usb: ehci: Prevent missed ehci interrupts with edge-triggered MSI

[David Jeffery <djeffery@redhat.com>]

On Wed, Jul 14, 2021 at 10:29 AM Alan Stern <stern@rowland.harvard.edu> wrote:
>
> On Wed, Jul 14, 2021 at 10:03:09AM -0400, David Jeffery wrote:

> >
> > diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
> > index 36f5bf6a0752..2283205d4b40 100644
> > --- a/drivers/usb/host/ehci-hcd.c
> > +++ b/drivers/usb/host/ehci-hcd.c
> > @@ -704,14 +704,18 @@ static irqreturn_t ehci_irq (struct usb_hcd *hcd)
> >  {
> >       struct ehci_hcd         *ehci = hcd_to_ehci (hcd);
> >       u32                     status, masked_status, pcd_status = 0, cmd;
> > +     u32                     current_status;
> >       int                     bh;
> >
> >       spin_lock(&ehci->lock);
> >
> > -     status = ehci_readl(ehci, &ehci->regs->status);
> > +     status = 0;
> >
> > +     current_status = ehci_readl(ehci, &ehci->regs->status);
> > +restart:
> > +     status |= current_status;
> >       /* e.g. cardbus physical eject */
> > -     if (status == ~(u32) 0) {
> > +     if (current_status == ~(u32) 0) {
> >               ehci_dbg (ehci, "device removed\n");
> >               goto dead;
> >       }
>
> Mild stylistic quibble: I generally prefer to have a blank line before a
> /* ... */ comment.  And it doesn't seem reasonable to have a blank line
> between "status = 0" and the current_status assignment, since those are
> similar once-only things before the beginning of the "restart" loop.
> Also, I would move the "status |= current_status" line after the test
> for device removed, since that test doesn't use status.
>
> But obviously none of these things affect the patch's correntness.

I'll update it with requested changes and resend it.

>
> You can choose to submit a new version of the patch with those stylistic
> changes, or if you prefer, just stick with this version.  Either way,
>
> Acked-by: Alan Stern <stern@rowland.harvard.edu>
>
> Does this issue affect any other PCI-based host controller drivers?
>
> Alan Stern
>

Possibly.  The uhci driver should have the same issue if hardware
exists with it and has MSI for it.  I suspect the ohci driver has a
similar issue, but I'm not familiar enough with its interfaces and
specification to say for sure.

David Jeffery